The present invention pertains to a rotary damper and particularly one which includes temperature compensation structure to control the torque for a wide range of operating temperatures.
Fluid filled viscous damping devices are becoming popular for use on a variety of vehicle accessories such as overhead storage bins, slide-out trays and the like. They allow, for example, a storage bin with a pivoted cover such as disclosed in U.S. Pat. No. 4,469,365 to be gradually lowered instead of dropping in an uncontrolled fashion. Similarly spring-loaded slides such as used in container holders or the like can also be coupled to a rotary damping device to control the slide motion as it is extended and retracted.
One difficulty with fluid filled viscous rotary damping devices is that in the vehicle environment wide temperature ranges are encountered. With a viscous fluid as the temperature decreases viscosity increases dramatically and correspondingly, as the temperature increases the viscosity decreases thereby resulting in an inconsistent feel to the vehicle accessory at different tempertures. With relatively low viscosity fluid such as lubricating oil used in internal combustion engines, multi-grade viscosity additives can be employed in an effort to control the viscosity with temperature changes. With relatively high viscosity material employed in fluid filled rotary dampers, the viscosity cannot be controlled in this manner. As a result, rotary dampers used in present vehicle accessories provide a compromised performance which varies widely with temperature fluctuations normally encountered in the vehicle environment.